/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.ocean.util;

import java.util.Arrays;
import java.io.Serializable;

/**
 * An "open" BitSet implementation that allows direct access to the array of
 * words storing the bits. <p/> Unlike java.util.bitet, the fact that bits are
 * packed into an array of longs is part of the interface. This allows efficient
 * implementation of other algorithms by someone other than the author. It also
 * allows one to efficiently implement alternate serialization or interchange
 * formats. <p/> <code>OpenBitSet</code> is faster than
 * <code>java.util.BitSet</code> in most operations and *much* faster at
 * calculating cardinality of sets and results of set operations. It can also
 * handle sets of larger cardinality (up to 64 * 2**32-1) <p/> The goals of
 * <code>OpenBitSet</code> are the fastest implementation possible, and
 * maximum code reuse. Extra safety and encapsulation may always be built on
 * top, but if that's built in, the cost can never be removed (and hence people
 * re-implement their own version in order to get better performance). If you
 * want a "safe", totally encapsulated (and slower and limited) BitSet class,
 * use <code>java.util.BitSet</code>. <p/>
 * <h3>Performance Results</h3>
 * 
 * Test system: Pentium 4, Sun Java 1.5_06 -server -Xbatch -Xmx64M <br/>BitSet
 * size = 1,000,000 <br/>Results are java.util.BitSet time divided by OpenBitSet
 * time. <table border="1">
 * <tr>
 * <th></th>
 * <th>cardinality</th>
 * <th>intersect_count</th>
 * <th>union</th>
 * <th>nextSetBit</th>
 * <th>get</th>
 * <th>iterator</th>
 * </tr>
 * <tr>
 * <th>50% full</th>
 * <td>3.36</td>
 * <td>3.96</td>
 * <td>1.44</td>
 * <td>1.46</td>
 * <td>1.99</td>
 * <td>1.58</td>
 * </tr>
 * <tr>
 * <th>1% full</th>
 * <td>3.31</td>
 * <td>3.90</td>
 * <td>&nbsp;</td>
 * <td>1.04</td>
 * <td>&nbsp;</td>
 * <td>0.99</td>
 * </tr>
 * </table> <br/> Test system: AMD Opteron, 64 bit linux, Sun Java 1.5_06
 * -server -Xbatch -Xmx64M <br/>BitSet size = 1,000,000 <br/>Results are
 * java.util.BitSet time divided by OpenBitSet time. <table border="1">
 * <tr>
 * <th></th>
 * <th>cardinality</th>
 * <th>intersect_count</th>
 * <th>union</th>
 * <th>nextSetBit</th>
 * <th>get</th>
 * <th>iterator</th>
 * </tr>
 * <tr>
 * <th>50% full</th>
 * <td>2.50</td>
 * <td>3.50</td>
 * <td>1.00</td>
 * <td>1.03</td>
 * <td>1.12</td>
 * <td>1.25</td>
 * </tr>
 * <tr>
 * <th>1% full</th>
 * <td>2.51</td>
 * <td>3.49</td>
 * <td>&nbsp;</td>
 * <td>1.00</td>
 * <td>&nbsp;</td>
 * <td>1.02</td>
 * </tr>
 * </table>
 * 
 * @author yonik
 * @version $Id$
 */

public class OpenBitSet implements Cloneable, Serializable {
	protected long[] bits;
	protected int wlen; // number of words (elements) used in the array

	public static void main(String[] args) {
		OpenBitSet bitSet = new OpenBitSet(1000000);
		System.out.println(bitSet.bits.length);
	}

	/**
	 * Constructs an OpenBitSet large enough to hold numBits.
	 * 
	 * @param numBits
	 */
	public OpenBitSet(long numBits) {
		bits = new long[bits2words(numBits)];
		wlen = bits.length;
	}

	public OpenBitSet() {
		this(64);
	}

	/**
	 * Constructs an OpenBitSet from an existing long[]. <br/> The first 64 bits
	 * are in long[0], with bit index 0 at the least significant bit, and bit
	 * index 63 at the most significant. Given a bit index, the word containing it
	 * is long[index/64], and it is at bit number index%64 within that word.
	 * <p>
	 * numWords are the number of elements in the array that contain set bits
	 * (non-zero longs). numWords should be &lt= bits.length, and any existing
	 * words in the array at position &gt= numWords should be zero.
	 * 
	 */
	public OpenBitSet(long[] bits, int numWords) {
		this.bits = bits;
		this.wlen = numWords;
	}

	/**
	 * Returns the current capacity in bits (1 greater than the index of the last
	 * bit)
	 */
	public long capacity() {
		return bits.length << 6;
	}

	/**
	 * Returns the current capacity of this set. Included for compatibility. This
	 * is *not* equal to {@link #cardinality}
	 */
	public long size() {
		return capacity();
	}

	/** Returns true if there are no set bits */
	public boolean isEmpty() {
		return cardinality() == 0;
	}

	/** Expert: returns the long[] storing the bits */
	public long[] getBits() {
		return bits;
	}

	/** Expert: sets a new long[] to use as the bit storage */
	public void setBits(long[] bits) {
		this.bits = bits;
	}

	/** Expert: gets the number of longs in the array that are in use */
	public int getNumWords() {
		return wlen;
	}

	/** Expert: sets the number of longs in the array that are in use */
	public void setNumWords(int nWords) {
		this.wlen = nWords;
	}

	/** Returns true or false for the specified bit index. */
	public boolean get(int index) {
		int i = index >> 6; // div 64
		// signed shift will keep a negative index and force an
		// array-index-out-of-bounds-exception, removing the need for an explicit
		// check.
		if (i >= bits.length)
			return false;

		int bit = index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		return (bits[i] & bitmask) != 0;
	}

	/**
	 * Returns true or false for the specified bit index. The index should be less
	 * than the OpenBitSet size
	 */
	public boolean fastGet(int index) {
		int i = index >> 6; // div 64
		// signed shift will keep a negative index and force an
		// array-index-out-of-bounds-exception, removing the need for an explicit
		// check.
		int bit = index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		return (bits[i] & bitmask) != 0;
	}

	/**
	 * Returns true or false for the specified bit index The index should be less
	 * than the OpenBitSet size
	 */
	public boolean get(long index) {
		int i = (int) (index >> 6); // div 64
		if (i >= bits.length)
			return false;
		int bit = (int) index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		return (bits[i] & bitmask) != 0;
	}

	/**
	 * Returns true or false for the specified bit index. Allows specifying an
	 * index outside the current size.
	 */
	public boolean fastGet(long index) {
		int i = (int) (index >> 6); // div 64
		int bit = (int) index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		return (bits[i] & bitmask) != 0;
	}

	/*
	 * // alternate implementation of get() public boolean get1(int index) { int i =
	 * index >> 6; // div 64 int bit = index & 0x3f; // mod 64 return
	 * ((bits[i]>>>bit) & 0x01) != 0; // this does a long shift and a bittest (on
	 * x86) vs // a long shift, and a long AND, (the test for zero is prob a
	 * no-op) // testing on a P4 indicates this is slower than (bits[i] & bitmask) !=
	 * 0; }
	 */

	/**
	 * returns 1 if the bit is set, 0 if not. The index should be less than the
	 * OpenBitSet size
	 */
	public int getBit(int index) {
		int i = index >> 6; // div 64
		int bit = index & 0x3f; // mod 64
		return ((int) (bits[i] >>> bit)) & 0x01;
	}

	/*
	 * public boolean get2(int index) { int word = index >> 6; // div 64 int bit =
	 * index & 0x0000003f; // mod 64 return (bits[word] << bit) < 0; // hmmm,
	 * this would work if bit order were reversed // we could right shift and
	 * check for parity bit, if it was available to us. }
	 */

	/** sets a bit, expanding the set size if necessary */
	public void set(long index) {
		int wordNum = expandingWordNum(index);
		int bit = (int) index & 0x3f;
		long bitmask = 1L << bit;
		bits[wordNum] |= bitmask;
	}

	/**
	 * Sets the bit at the specified index. The index should be less than the
	 * OpenBitSet size.
	 */
	public void fastSet(int index) {
		int wordNum = index >> 6; // div 64
		int bit = index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		bits[wordNum] |= bitmask;
	}

	/**
	 * Sets the bit at the specified index. The index should be less than the
	 * OpenBitSet size.
	 */
	public void fastSet(long index) {
		int wordNum = (int) (index >> 6);
		int bit = (int) index & 0x3f;
		long bitmask = 1L << bit;
		bits[wordNum] |= bitmask;
	}

	protected int expandingWordNum(long index) {
		int wordNum = (int) (index >> 6);
		if (wordNum >= wlen) {
			ensureCapacity(index + 1);
			wlen = wordNum + 1;
		}
		return wordNum;
	}

	/**
	 * clears a bit. The index should be less than the OpenBitSet size.
	 */
	public void fastClear(int index) {
		int wordNum = index >> 6;
		int bit = index & 0x03f;
		long bitmask = 1L << bit;
		bits[wordNum] &= ~bitmask;
		// hmmm, it takes one more instruction to clear than it does to set... any
		// way to work around this? If there were only 63 bits per word, we could
		// use a right shift of 10111111...111 in binary to position the 0 in the
		// correct place (using sign extension).
		// Could also use Long.rotateRight() or rotateLeft() *if* they were
		// converted
		// by the JVM into a native instruction.
		// bits[word] &= Long.rotateLeft(0xfffffffe,bit);
	}

	/**
	 * clears a bit. The index should be less than the OpenBitSet size.
	 */
	public void fastClear(long index) {
		int wordNum = (int) (index >> 6); // div 64
		int bit = (int) index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		bits[wordNum] &= ~bitmask;
	}

	/** clears a bit, allowing access beyond the current set size */
	public void clear(long index) {
		int wordNum = (int) (index >> 6); // div 64
		if (wordNum >= wlen)
			return;
		int bit = (int) index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		bits[wordNum] &= ~bitmask;
	}

	/**
	 * Sets a bit and returns the previous value. The index should be less than
	 * the OpenBitSet size.
	 */
	public boolean getAndSet(int index) {
		int wordNum = index >> 6; // div 64
		int bit = index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		boolean val = (bits[wordNum] & bitmask) != 0;
		bits[wordNum] |= bitmask;
		return val;
	}

	/**
	 * Sets a bit and returns the previous value. The index should be less than
	 * the OpenBitSet size.
	 */
	public boolean getAndSet(long index) {
		int wordNum = (int) (index >> 6); // div 64
		int bit = (int) index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		boolean val = (bits[wordNum] & bitmask) != 0;
		bits[wordNum] |= bitmask;
		return val;
	}

	/**
	 * flips a bit. The index should be less than the OpenBitSet size.
	 */
	public void fastFlip(int index) {
		int wordNum = index >> 6; // div 64
		int bit = index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		bits[wordNum] ^= bitmask;
	}

	/**
	 * flips a bit. The index should be less than the OpenBitSet size.
	 */
	public void fastFlip(long index) {
		int wordNum = (int) (index >> 6); // div 64
		int bit = (int) index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		bits[wordNum] ^= bitmask;
	}

	/** flips a bit, expanding the set size if necessary */
	public void flip(long index) {
		int wordNum = expandingWordNum(index);
		int bit = (int) index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		bits[wordNum] ^= bitmask;
	}

	/**
	 * flips a bit and returns the resulting bit value. The index should be less
	 * than the OpenBitSet size.
	 */
	public boolean flipAndGet(int index) {
		int wordNum = index >> 6; // div 64
		int bit = index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		bits[wordNum] ^= bitmask;
		return (bits[wordNum] & bitmask) != 0;
	}

	/**
	 * flips a bit and returns the resulting bit value. The index should be less
	 * than the OpenBitSet size.
	 */
	public boolean flipAndGet(long index) {
		int wordNum = (int) (index >> 6); // div 64
		int bit = (int) index & 0x3f; // mod 64
		long bitmask = 1L << bit;
		bits[wordNum] ^= bitmask;
		return (bits[wordNum] & bitmask) != 0;
	}

	/**
	 * Flips a range of bits, expanding the set size if necessary
	 * 
	 * @param startIndex
	 *          lower index
	 * @param endIndex
	 *          one-past the last bit to flip
	 */
	public void flip(long startIndex, long endIndex) {
		if (endIndex <= startIndex)
			return;

		int oldlen = wlen;
		ensureCapacity(endIndex);
		int startWord = (int) (startIndex >> 6);
		int endWord = (int) (endIndex >> 6);

		/***************************************************************************
		 * * Grrr, java shifting wraps around so -1L>>64 == -1 long startmask = -1L <<
		 * (startIndex & 0x3f); // example: 11111...111000 long endmask = -1L >>>
		 * (64-(endIndex & 0x3f)); // example: 00111...111111
		 **************************************************************************/

		long startmask = -1L << startIndex;
		long endmask = (endIndex & 0x3f) == 0 ? 0 : -1L >>> (64 - endIndex);

		if (this.wlen <= endWord) {
			this.wlen = endWord;
			if (endmask != 0)
				this.wlen++;
		}

		if (startWord == endWord) {
			bits[startWord] ^= (startmask & endmask);
			return;
		}

		bits[startWord] ^= startmask;

		int middle = Math.min(oldlen, endWord);
		for (int i = startWord + 1; i < middle; i++) {
			bits[i] = ~bits[i];
		}

		if (endWord > middle) {
			Arrays.fill(bits, middle, endWord, -1L);
		}

		if (endmask != 0) {
			bits[endWord] ^= endmask;
		}
	}

	/*
	 * public static int pop(long v0, long v1, long v2, long v3) { // derived from
	 * pop_array by setting last four elems to 0. // exchanges one pop() call for
	 * 10 elementary operations // saving about 7 instructions... is there a
	 * better way? long twosA=v0 & v1; long ones=v0^v1;
	 * 
	 * long u2=ones^v2; long twosB =(ones&v2)|(u2&v3); ones=u2^v3;
	 * 
	 * long fours=(twosA&twosB); long twos=twosA^twosB;
	 * 
	 * return (pop(fours)<<2) + (pop(twos)<<1) + pop(ones);
	 *  }
	 */

	/** @return the number of set bits */
	public long cardinality() {
		return BitUtil.pop_array(bits, 0, wlen);
	}

	/**
	 * Returns the popcount or cardinality of the intersection of the two sets.
	 * Neither set is modified.
	 */
	public static long intersectionCount(OpenBitSet a, OpenBitSet b) {
		return BitUtil.pop_intersect(a.bits, b.bits, 0, Math.min(a.wlen, b.wlen));
	}

	/**
	 * Returns the popcount or cardinality of the union of the two sets. Neither
	 * set is modified.
	 */
	public static long unionCount(OpenBitSet a, OpenBitSet b) {
		long tot = BitUtil.pop_union(a.bits, b.bits, 0, Math.min(a.wlen, b.wlen));
		if (a.wlen < b.wlen) {
			tot += BitUtil.pop_array(b.bits, a.wlen, b.wlen - a.wlen);
		} else if (a.wlen > b.wlen) {
			tot += BitUtil.pop_array(a.bits, b.wlen, a.wlen - b.wlen);
		}
		return tot;
	}

	/**
	 * Returns the popcount or cardinality of "a and not b" or "intersection(a,
	 * not(b))". Neither set is modified.
	 */
	public static long andNotCount(OpenBitSet a, OpenBitSet b) {
		long tot = BitUtil.pop_andnot(a.bits, b.bits, 0, Math.min(a.wlen, b.wlen));
		if (a.wlen > b.wlen) {
			tot += BitUtil.pop_array(a.bits, b.wlen, a.wlen - b.wlen);
		}
		return tot;
	}

	/**
	 * Returns the popcount or cardinality of the exclusive-or of the two sets.
	 * Neither set is modified.
	 */
	public static long xorCount(OpenBitSet a, OpenBitSet b) {
		long tot = BitUtil.pop_xor(a.bits, b.bits, 0, Math.min(a.wlen, b.wlen));
		if (a.wlen < b.wlen) {
			tot += BitUtil.pop_array(b.bits, a.wlen, b.wlen - a.wlen);
		} else if (a.wlen > b.wlen) {
			tot += BitUtil.pop_array(a.bits, b.wlen, a.wlen - b.wlen);
		}
		return tot;
	}

	/**
	 * Returns the index of the first set bit starting at the index specified. -1
	 * is returned if there are no more set bits.
	 */
	public int nextSetBit(int index) {
		int i = index >> 6;
		if (i >= wlen)
			return -1;
		int subIndex = index & 0x3f; // index within the word
		long word = bits[i] >> subIndex; // skip all the bits to the right of index

		if (word != 0) {
			return (i << 6) + subIndex + BitUtil.ntz(word);
		}

		while (++i < wlen) {
			word = bits[i];
			if (word != 0)
				return (i << 6) + BitUtil.ntz(word);
		}

		return -1;
	}

	/**
	 * Returns the index of the first set bit starting at the index specified. -1
	 * is returned if there are no more set bits.
	 */
	public long nextSetBit(long index) {
		int i = (int) (index >>> 6);
		if (i >= wlen)
			return -1;
		int subIndex = (int) index & 0x3f; // index within the word
		long word = bits[i] >>> subIndex; // skip all the bits to the right of index

		if (word != 0) {
			return (((long) i) << 6) + (subIndex + BitUtil.ntz(word));
		}

		while (++i < wlen) {
			word = bits[i];
			if (word != 0)
				return (((long) i) << 6) + BitUtil.ntz(word);
		}

		return -1;
	}

	public Object clone() {
		OpenBitSet obs = new OpenBitSet();
		obs.wlen = wlen;
		obs.bits = Arrays.copyOf(obs.bits, obs.bits.length);
		return obs;
	}

	/** this = this AND other */
	public void intersect(OpenBitSet other) {
		int newLen = Math.min(this.wlen, other.wlen);
		long[] thisArr = this.bits;
		long[] otherArr = other.bits;
		// testing against zero can be more efficient
		int pos = newLen;
		while (--pos >= 0) {
			thisArr[pos] &= otherArr[pos];
		}
		if (this.wlen > newLen) {
			// fill zeros from the new shorter length to the old length
			Arrays.fill(bits, newLen, this.wlen, 0);
		}
		this.wlen = newLen;
	}

	/** this = this OR other */
	public void union(OpenBitSet other) {
		int newLen = Math.max(wlen, other.wlen);
		ensureCapacityWords(newLen);

		long[] thisArr = this.bits;
		long[] otherArr = other.bits;
		int pos = Math.min(wlen, other.wlen);
		while (--pos >= 0) {
			thisArr[pos] |= otherArr[pos];
		}
		if (this.wlen < newLen) {
			System.arraycopy(otherArr, this.wlen, thisArr, this.wlen, newLen - this.wlen);
		}
		this.wlen = newLen;
	}

	/** Remove all elements set in other. this = this AND_NOT other */
	public void remove(OpenBitSet other) {
		int idx = Math.min(wlen, other.wlen);
		long[] thisArr = this.bits;
		long[] otherArr = other.bits;
		while (--idx >= 0) {
			thisArr[idx] &= ~otherArr[idx];
		}
	}

	/** this = this XOR other */
	public void xor(OpenBitSet other) {
		int newLen = Math.max(wlen, other.wlen);
		ensureCapacityWords(newLen);

		long[] thisArr = this.bits;
		long[] otherArr = other.bits;
		int pos = Math.min(wlen, other.wlen);
		while (--pos >= 0) {
			thisArr[pos] ^= otherArr[pos];
		}
		if (this.wlen < newLen) {
			System.arraycopy(otherArr, this.wlen, thisArr, this.wlen, newLen - this.wlen);
		}
		this.wlen = newLen;
	}

	// some BitSet compatability methods

	// ** see {@link intersect} */
	public void and(OpenBitSet other) {
		intersect(other);
	}

	// ** see {@link union} */
	public void or(OpenBitSet other) {
		union(other);
	}

	// ** see {@link andNot} */
	public void andNot(OpenBitSet other) {
		remove(other);
	}

	/** returns true if the sets have any elements in common */
	public boolean intersects(OpenBitSet other) {
		int pos = Math.min(this.wlen, other.wlen);
		long[] thisArr = this.bits;
		long[] otherArr = other.bits;
		while (--pos >= 0) {
			if ((thisArr[pos] & otherArr[pos]) != 0)
				return true;
		}
		return false;
	}

	/**
	 * Expand the long[] with the size given as a number of words (64 bit longs).
	 * getNumWords() is unchanged by this call.
	 */
	public void ensureCapacityWords(int numWords) {
		if (bits.length < numWords) {
			long[] newBits = new long[numWords];
			System.arraycopy(bits, 0, newBits, 0, wlen);
			bits = newBits;
		}
	}

	/**
	 * Ensure that the long[] is big enough to hold numBits, expanding it if
	 * necessary. getNumWords() is unchanged by this call.
	 */
	public void ensureCapacity(long numBits) {
		ensureCapacityWords(bits2words(numBits));
	}

	/**
	 * Lowers numWords, the number of words in use, by checking for trailing zero
	 * words.
	 */
	public void trimTrailingZeros() {
		int idx = wlen - 1;
		while (idx >= 0 && bits[idx] == 0)
			idx--;
		wlen = idx + 1;
	}

	/** returns the number of 64 bit words it would take to hold numBits */
	public static int bits2words(long numBits) {
		return (int) (((numBits - 1) >>> 6) + 1);
	}

	/** returns true if both sets have the same bits set */
	public boolean equals(Object o) {
		if (this == o)
			return true;
		if (!(o instanceof OpenBitSet))
			return false;
		OpenBitSet a;
		OpenBitSet b = (OpenBitSet) o;
		// make a the larger set.
		if (b.wlen > this.wlen) {
			a = b;
			b = this;
		} else {
			a = this;
		}

		// check for any set bits out of the range of b
		for (int i = a.wlen - 1; i >= b.wlen; i--) {
			if (a.bits[i] != 0)
				return false;
		}

		for (int i = b.wlen - 1; i >= 0; i--) {
			if (a.bits[i] != b.bits[i])
				return false;
		}

		return true;
	}

	public int hashCode() {
		long h = 0x98761234; // something non-zero for length==0
		for (int i = bits.length; --i >= 0;) {
			h ^= bits[i];
			h = (h << 1) | (h >>> 31); // rotate left
		}
		return (int) ((h >> 32) ^ h); // fold leftmost bits into right
	}

}
